Electric heaters



March 5, 1963 A. c. BOGGS ELECTRIC HEATERS Filed Nov. 22, 1960 2 Sheets-$heet 2 INVENTOR C. 50665 )"1 a; ALBEN United States 3,089,543 ELECTRIC HEATERS Boggs, Pittsburgh, Pa., assignor to Edwin L. Wiegand Company, Pittsburgh, Pa. Filed Nov. 22, 1960, Ser. No. 71,082 1 Claim. (Cl. 338-273) Alben C.

The present invention relates to electric heaters, more particularly to electric heaters of the type known as cartridge heaters, and the principal object of the invention is to provide new and improved heaters of the character described.

Cartridge heaters of the type wherein a tubular sheath encloses a resistor coil embedded in compacted electricinsulating, heat-conductive material and wherein a pair of terminal conductors project outwardly of an end of the sheath and are connected to respective coil ends have long heater to compact the contained material about the resistor coil and the terminal conductors, be employed to effectuate certain electrical connections within the sheath. While this proposal has been meritorious, in practice the prior art constructions have not been satisfactory since consistently good electrical connections have been difficult to achieve.

The present invention advantageously utilizes the swaging' operation, or other equivalent mode of compacting the electric-insulating, heat-conductive material within the sheath, to provide suitable electrical connections there- .within which are consistently satisfactory. Other advantages will readily become apparent from a study of the following description and from the drawings appended .hereto.

In the drawings accompanying this specification and forming a part of this application there is shown, for purpose of illustration, embodiments which the invention may assume, and in these drawings:

FIGURE 1 is-a view in longitudinal section through -a cartridge heating element constructed in accordance with the present invention,

FIGURE 2 is a view similar to FIGURE 1 but at a preliminary stage of manufacture,

FIGURE 3 is an enlarged, exploded fragmentary perspective view of certain details seen in FIGURE 2,

FIGURE 4 is an enlarged, fragmentary transverse sectional view of one of the details seen in FIGURE 3, and

FIGURE 5 is a reduced size view similar to FIGURE 2 but of a modified structure.

With reference to FIGURE 1, there is illustrated a cartridge heater in substantially final form constructed in accordance with the present invention. Such heater is herein shown to comprise a tubular metal sheath Ill closed at the left end by an inwardly dished, metallic disk 11. Disposed within the sheath and in radially spaced relation with the interior thereof is a coiled resistor 12. Re spective ends of the resistor coil are welded or otherwise connected to the short leg 13 of respective U-shaped, electrically-conductive metal strips 14. The long leg 15 of each strip 14 is disposed within the resistor coil and extends longitudinally thereof for a purpose to appear.

Also disposed within the resistor coil in spaced, sideby-side relation are a pair of terminal conductor pins 16 which project outwardly of the right, or open end of the sheath for connection to a source of electrical energy. Each terminal pin is coextensive with the leg 15 of refiddiihfid Patented Mar. 5, 1963 spective strips 14 and is in tight engagement therewith to provide a low-resistance, electrical connection therebetween. The interior of the sheath is filled with a suitable, highly compacted, electric-insulating, heat-conductive material 17 such as magnesium oxide which immobilizes the various parts above described. A thin, flexible washer 18 of, for example, mica or the like may abut the material 17 at the open end of the sheath to prevent loss of such material through the open sheath end. If desired, the pocket shown at the open end of the sheath may be filled with a suitable cement or the like in the well-known manner to further close such sheath open end.

Referring now to FiGURE 2 wherein the heater thus far described is shown during a preliminary stage of assembly, it will he noted that the sheath in at this stage is shorter and larger in diameter than is shown in FIG- URE 1. Disk 11, at this time, but loosely closes the left end of the sheath, the disk being seated against a radially inwardly turned sheath end portion 19.

The resistor coil 12 is wound upon the periphery of a frangible, dielectric body 20 formed, for example, of magnesium oxide powder held together by means of a suitable binder. The outside diameter of this body is somewhat smaller than the interior of the sheath so that the resistor coil on the body exterior will be spaced from the sheath interior. Extending from end to end of the body 20 are openings 21 in spaced, side-by-side relation. As illustrated, such openings provide for the reception of respective terminal pins 16 and legs 15 of respective strips 14.

An important feature of the present invention is the cross-sectional configuration of the body openings 21 and that of the strip legs 15. As best seen in FIGURE 3, pins 16 are round in cross-section while strip leg 15 is arcuate in cross-section to closely fit with the pin and partially embrace the latter. Openings 21 are formed to closely fit about the pins and the strip legs 15 and to this end, each opening (see especially FIGURE 4) has a relatively large, arcuate defining margin 22 for closely receiving a respective strip leg 15 and an opposed, relatively small, arcuate defining margin 23 for closely receiving a respective terminal pin 16. The importance of so forming the strip legs and the body openings will hereinafter appear.

The construction thus far disclosed may conveniently be assembled by inserting one of the strips 14 in one end of a body opening 21 so that the strip leg 13 overlies the periphery of the body at one end of the latter. The resistor 12, one end of which was preferably welded or otherwise secured to the leg 13 of the aforesaid strip 14 prior to its insertion in the body opening, may then be wound to coil form on the exterior of the body 2th from said one end to the other. The other strip 14 may then be inserted into the other body opening from the opposite end of the body with its leg 13 overlying the body periphery. The adjoining end of the resistor may then be welded or otherwise secured to such strip leg 13 to retain the resistor coil assembled with the body. It will be understood, of course, that each strip leg 15 Will be disposed in the portion 22 of its opening 21.

Terminal pins 16 may then be inserted into body openings 21 to close fitting engagement with respective strips 14. Note that the considerable length of strip leg portions 15 insures an adequate area of contact between the strips and the pins as does the pin-embracing, cross-sectional configuration of such legs. For reasons to appear, pins 16 are so inserted into the body openings that their ends 116 project beyond the body a slight amount.

With the resistor 12, the pins 16 and the strips 14 assembled with the body 2%} as above described, such assembly may be inserted into the open end or" the sheath with the 'body end containing the terminal pin portions 116 foremost. Prior to such insertion of the body, a member 24, preferably of the same frangible material as body 20, will be disposed for interposition between the disk 11 and the body 20, Such member presently has an outside diameter closely fitting the sheath interior and has a pair of recesses 25, see FIGURE 3, in the face adjacent the body for closely receiving respective terminal pin ends 116.

Following disposition of the assembled body 20 within the sheath (as seen in FIGURE 2) with the member '24 interposed-between thebody and the disk 11, a second member 26 (see also FIGURE 3) will be disposed against that end, of the bodyadjacent the open end of the sheath. This member also is preferably formed of the same frangible material as body 20 and has a pair (if-through apertures 27 for passing respective terminal pins. Member 26 is similar to 24 in that it too is proportioned to closely fit within the sheath; however, a plurality of notches 28 are provided in its periphery for. a purpose to appear; 7 I

With the parts assembled as seen in FIGURE 2, it will be noted that the body 20 is maintained centered within the sheath by means of the interengagernent. of the members 24, 26' with the sheath interior and their interengagement with the terminal, pins 16 extending through the body. Accordingly, the sheath may now be filled with powdered material, such as magnesium oxide, through its open end. Note that the notches 23 in the periphery of the member- 26 permit entrance of such material.

If desired, member 24' may also be formed with 'peripheral notches (not shown) similar to those, formed in the member 26 to perm-it the powdered material to fill the voids between the member 24 and the disk '11,.

After the sheath has been filled to the level of the member 26, the mica washer 18 may be installed to prevent escape of the powdered material. The unit will next be subjected to a swaglng or other operation which re,-

duces its transverse size an amount to fragment the body 29 and the members 24, 26 and to pack the powdered material, together with that which is fragmented, to a generally homogenous mass of rock-like hardness in which the resistor, the strips and the terminal pins are'embed-ded'.

In accordance with well-known practice, removable plugs may be inserted in one or both ends of the sheath during this compacting operation to insure against loss of any of the contained material. As aresultof this com.- pacting operation, the sheath will be reducedin transverse size and also elongated as may be seen by a comparison of FIGURESv 1 and 2. Also, as a result of this operation, the dished disk 11 will be tightly crimped in the left end' of the sheathto close the latter.

It is to be understood that the vibration of the. swaging operation together with the fragmentation of the body 20 tends to cause a slight shifting of the terminal pins and theother parts within the sheath. In some prior art con structions this sometimes resulted in aloss of electrical continuity between the pins and the resistor. With the present construction, however, wherein the strips-1 4 partially embrace the pins, fragmented pieces of the body cannot wedge the pins and the strips apart thus causing such continuity loss.

An important advantage in forming: heaters in accordance with the present invention is that merely by employing longer terminal pins and a longer sheath, a series of bodies may be strung upon. the pins to. provide heaters of greater heatoutput. Thus, as shown in FIGURE 5, two bodies 20a (similar in all respects to body 20) may be disposed'in end to end relation'with terminal pins 16a extending through their aligned openings. As will be obvious, the resistors 12;: carried by respective bodies 20;: will be connected together inparallel so that a failure of one resistor will notatfect operation of the other; Note that a second member 26a is interposed between the two bodiesZOa to insure concentricity of the bodies with the sheath interior. While FIGURE 5' illustrates a heater employing but two bodies, there isno limit to the number that could be employed by following the above teachlIlgS.

In viewof the foregoing itwill {be apparent to those skilled in the art that'l have'accomplished at least the principal object: of my invention and it will also be apparent to those skilled in the art that the embodiments herein described maybe variously changed and modified, without departing from the spirit of the invention, and that the invention is capable of uses and has advantages not herein specifically described; hence itwill be appreciated that the herein disclosed embodiments are illustrative only, and that my invention isnot limited thereto.

I claim:

An electric heatingelement, comprising a metal sheath substantiallyfilled with'electric insulating material, a. resistor and a terminal pin embedded within said insulating material, and a lowresistance conductor of stripmetal electrically connected to said resistorand also embedded within said insulating material, said-conductor havin'g'a -le'gcoextensive with andcontacting said pin over a considerable length thereof, saidleg beingofj'a cross-sectional shape and size complementary to the shape and size or.

References Cited. in the fil'erof this patent UNITED STATES'VPATENTS 2. m 1 .19 5 2,527,026 Mucher ova e-4,, 1950 Shaw May 22,1954 

